Automatic image feature removal

ABSTRACT

Apparatus and methods are described including receiving, via a computer processor, at least one image of a portion of a subject&#39;s body. One or more features that are present within the image of the portion of the subject&#39;s body, and that were artificially added to the image subsequent to acquisition of the image, are identified. In response thereto, an output is generated on an output device.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is the U.S. National Phase application under 35 U.S.C.§ 371 of International Application No. PCT/EP2016/071362, filed on Sep.9, 2016, which claims the benefit of U.S. Provisional Application No.62/216,574, filed on Sep. 10, 2015. These applications are herebyincorporated by reference herein.

FIELD OF EMBODIMENTS OF THE INVENTION

Some applications of the present invention generally relate to automaticimage processing. Specifically, some applications of the presentinvention relate to medical imaging and analysis of such images.

BACKGROUND

Medical imaging is used to treat and diagnose diseases. There are alarge number of imaging modalities that are used to generate medicalimages, including video, fluoroscopy, angiography, ultrasound, CT, MR,PET, PET-CT, CT angiography, SPECT, Gamma camera imaging, OpticalCoherence Tomography (OCT), Near-Infra-Red Spectroscopy (NIRS),Vibration Response Imaging (VRI), optical imaging, infrared imaging,electrical mapping imaging, other forms of functional imaging, FocusedAcoustic Computed Tomography (FACT), Optical Frequency Domain Imaging(OFDI). Many medical imaging systems are configured to add features(e.g., icons, and/or alphanumeric features) to images that have beenacquired by the image-acquisition unit of the system. For example, suchdata may include information regarding the subject of the imaging,and/or data relating to measurements that have been performed upon theimage.

SUMMARY OF EMBODIMENTS

For some applications of the present invention, a computer processorreceives an image of a portion of a subject's body from animage-processing system. The computer processor identifies features thatare present within the image that were artificially added to the imageby the image-processing system, subsequent to acquisition of the image.In response thereto, the computer processor generates an output on anoutput device. For example, the computer processor may drive a displayto display the image with the identified features removed from thedisplayed image. Alternatively or additionally, the computer processormay perform measurements upon the image, and may exclude the identifiedfeatures from being included in the measurements. The computer processormay then generate an indication of the measurements upon the outputdevice.

The artificially-added features that are identified by the computerprocessor may include features that are added by the image-processingsystem in order to identify the subject, to show measured dataassociated with the subject, to identify the image processing system(for example, the image may include a logo associated with themanufacturer of the image-processing system), to classify the image as acertain type of image, or to perform a different function. The featuresmay include alphanumeric characters, icons, pictures, and/or any othertype or shape of feature. Many medical imaging systems are configured toadd such features (e.g., icons, and/or alphanumeric data) to images thathave been acquired by an imaging device. For some applications, thecomputer processor identifies the artificially-added features byidentifying features within the image that have alphanumericcharacteristics.

There is therefore provided, in accordance with some applications of thepresent invention, a method including:

receiving, via at least one computer processor, at least one image of aportion of a subject's body;

using the at least one computer processor, identifying one or morefeatures that are present within the image of the portion of thesubject's body that were artificially added to the image, subsequent toacquisition of the image; and

in response thereto, generating an output on an output device.

For some applications, generating the output on the output deviceincludes driving a display to display the image with the identifiedfeatures removed from the displayed image.

For some applications, the method further comprises using the computerprocessor, performing measurements upon the image, by excluding theidentified features from being included in the measurements, andgenerating the output includes generating an indication of themeasurements upon the output device.

For some applications, identifying the one or more features includesdetermining that the one or more features are located within a givendistance of an edge of the image, and identifying the one or morefeatures as having been artificially added to the image, subsequent toacquisition of the image, at least partially in response thereto.

For some applications, identifying the one or more features includesidentifying one or more features that have alphanumeric characteristicsthat are present within the image.

For some applications, identifying the one or more features includesidentifying a set of pixels as defining a line and identifying the setof pixels as corresponding to a feature that has been artificially addedto the image subsequent to acquisition of the image, at least partiallyin response thereto.

For some applications, identifying the one or more features includesidentifying a region of the image within which a density of straightlines exceeds a threshold and identifying the region as containing afeature that has been artificially added to the image subsequent toacquisition of the image, at least partially in response thereto.

For some applications, identifying the one or more features includesdetermining that a density of horizontal and vertical gradients within agiven region of the image exceeds a threshold and identifying the regionas containing a feature that has been artificially added to the imagesubsequent to acquisition of the image, at least partially in responsethereto.

For some applications, identifying the one or more features includes:

determining that, in the image, a difference in intensity between afirst pixel and at least one second pixel within a given distance fromthe first pixel exceeds a threshold;

determining that a difference in intensity between a value of the firstpixel in the image and a value of the first pixel in one or moreadditional images of the portion of the subject's body is less than athreshold amount; and

identifying a region that contains the first pixel as containing afeature that has been artificially added to the image subsequent toacquisition of the image, at least partially in response thereto.

There is further provided, in accordance with some applications of thepresent invention, apparatus including:

an imaging device configured to acquire an image of a portion of a bodyof a subject;

an output device; and

at least one computer processor configured to:

-   -   receive the image of the portion of the subject's body;    -   determine that one or more features are present within the image        of the portion of the subject's body that were artificially        added to the image, subsequent to acquisition of the image by        the imaging device; and    -   in response thereto, generate an output on the output device.

For some applications, the computer processor is configured to generatethe output by driving a display to display the image with the identifiedfeatures removed from the displayed image.

For some applications, the computer processor is configured to performmeasurements upon the image, by excluding the identified features frombeing included in the measurements, and the computer processor isconfigured to generate the output by generating an indication of themeasurements upon the output device.

For some applications, the computer processor is configured to identifythe one or more features by determining that the one or more featuresare located within a given distance of an edge of the image, andidentifying the one or more features as having been artificially addedto the image, subsequent to acquisition of the image, at least partiallyin response thereto.

For some applications, the computer processor is configured to identifythe one or more features by identifying one or more features that havealphanumeric characteristics that are present within the image.

For some applications, the computer processor is configured to identifythe one or more features by identifying a set of pixels as defining aline and identifying the set of pixels as corresponding to a featurethat has been artificially added to the image subsequent to acquisitionof the image, at least partially in response thereto.

For some applications, the computer processor is configured to identifythe one or more features by identifying a region of the image withinwhich a density of straight lines exceeds a threshold and identifyingthe region as containing a feature that has been artificially added tothe image subsequent to acquisition of the image, at least partially inresponse thereto.

For some applications, the computer processor is configured to identifythe one or more features by determining that a density of horizontal andvertical gradients within a given region of the image exceeds athreshold and identifying the region as containing a feature that hasbeen artificially added to the image subsequent to acquisition of theimage, at least partially in response thereto.

For some applications, the computer processor is configured to identifythe one or more features by:

determining that, in the image, a difference in intensity between afirst pixel and at least one second pixel within a given distance fromthe first pixel exceeds a threshold;

determining that a difference in intensity between a value of the firstpixel in the image and a value of the first pixel in one or moreadditional images of the portion of the subject's body is less than athreshold amount; and

identifying a region that contains the first pixel as containing afeature that has been artificially added to the image subsequent toacquisition of the image, at least partially in response thereto.

There is additionally provided, in accordance with some applications ofthe present invention, a computer software product, for use with animaging device configured to acquire an image of a portion of a body ofa subject, and an output device, the computer software product includinga non-transitory computer-readable medium in which program instructionsare stored, which instructions, when read by a computer cause thecomputer to perform the steps of: receiving at least one image of aportion of a subject's body; identifying one or more features that arepresent within the image of the portion of the subject's body that wereartificially added to the image, subsequent to acquisition of the image;and, in response thereto, generating an output on the output device.

The present invention will be more fully understood from the followingdetailed description of embodiments thereof, taken together with thedrawings, in which:

BRIEF DESCRIPTION OF THE D WINGS

FIG. 1 is a schematic illustration of apparatus that is used in acatheterization laboratory, in accordance with some applications of thepresent invention;

FIG. 2 is an example of an extraluminal fluoroscopic image of asubject's chest that is image-processed by a computer processor, inaccordance with some applications of the present invention;

FIGS. 3A-B are flowcharts showing steps of an algorithm that isperformed by a processor, in accordance with some applications of thepresent invention;

FIGS. 4A-C are examples of binary images that are generated by applyingsteps of the flowchart shown in FIG. 3B to the image shown in FIG. 2, inaccordance with some applications of the present invention;

FIG. 4D is a mask image that was generated by combining the binaryimages shown in FIGS. 4A-C, in accordance with some applications of thepresent invention; and

FIG. 5 a flowchart showing steps of an algorithm that is performed by aprocessor, in accordance with some applications of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to FIG. 1, which is a schematic illustration ofapparatus that is used in a catheterization laboratory, in accordancewith some applications of the present invention. Typically, a subject isimaged using an extraluminal imaging device (i.e., an extraluminalimage-acquisition device) 20, which may include a fluoroscope thatacquires fluoroscopic images under regular mode (in the absence ofcontrast agent in the blood vessels of the subject that are beingimaged) and/or under angiographic mode (while there is a presence ofcontrast agent in the blood vessels of the subject that are beingimaged). For some applications, the imaging device performs fluoroscopy,CT, MR, PET, SPECT, ultrasound, or any combination thereof.

FIG. 1 additionally shows a guide catheter 22 that has been insertedinto a blood vessel of the subject (e.g., a coronary artery of thesubject) over a guidewire 24. An endoluminal medical device 26 has beeninserted into the subject's blood vessel (e.g., the subject's coronaryartery) through the guide catheter and over the guidewire.

For some applications, endoluminal medical device 26 includes anendoluminal data-acquisition device that is configured to acquire data(e.g., functional data or images) from inside the subject's bloodvessels. For some applications, the endoluminal data-acquisition deviceis an imaging probe. For some applications, the imaging probe is an IVUSprobe, an EBUS probe, a different type of ultrasound probe, an OCTprobe, an NIRS probe, an MR probe, a FACT probe, an OFDI probe, or anycombination thereof. For some applications, the endoluminaldata-acquisition device performs additional functions. For example, theendoluminal data-acquisition device may comprise a probe, such as theVIBE™ RX Vascular Imaging Balloon Catheter, marketed by VolcanoCorporation (San Diego, USA), that includes both IVUS and coronaryballoon functionalities.

For some applications, the endoluminal data-acquisition device acquiresdata in a form other than images. For example, the data may include datarelated to pressure, flow, temperature, electrical activity,oxygenation, biochemical composition, or any combination thereof. Forsome applications, and typically when data are acquired with respect toa coronary vessel, the endoluminal data-acquisition device is aFractional Flow Reserve (FFR) probe, and/or an instantaneous wave-freeratio (iFR) probe. For some applications, FFR and/or iFR measurementsare determined by performing image-processing on extraluminal images,and the derived FFR and/or iFR measurements are co-registered withendoluminal images of the lumen, using techniques described herein. Forsome applications, FFR and/or iFR measurements are determined byperforming image-processing on endoluminal images, and the derived FFRand/or iFR measurements are co-registered with extraluminal images ofthe lumen, using techniques described herein. For some applications,endoluminal images are co-registered with extraluminal images of thelumen, using techniques described herein, and FFR and/or iFRmeasurements are determined by performing image-processing on theco-registered images.

A computer processor 28 typically receives and processes images (e.g.,extraluminal images or endoluminal images). The computer processorcommunicates with a memory 29. Via a user interface 30, a user (e.g., aphysician and/or a catheterization laboratory technician) sendsinstructions to the computer processor. For some applications, the userinterface includes a keyboard 32, a mouse 34, a joystick 36, atouchscreen device 38 (such as a smartphone or a tablet computer), atouchpad, a trackball, a voice-command interface, and/or other types ofuser interfaces that are known in the art. Typically, the computerprocessor generates an output using an output device 40. Furthertypically, the output device includes a display, such as a monitor (asshown in FIG. 1), and the output includes an output that is displayed onthe display. For some applications, the display includes a head-updisplay and/or a head-mounted display, such as Google Glass®. For someapplications, the processor generates an output on a different type ofvisual, text, graphics, tactile, audio, and/or video output device,e.g., speakers, headphones, a smartphone, or a tablet computer. For someapplications, user interface 30 acts as both an input device and anoutput device. For some applications, the processor generates an outputon a computer-readable medium (e.g., a non-transitory computer-readablemedium), such as a disk, or a portable USB drive.

It is noted that, for some applications, more than one computerprocessor is used to perform the functions described herein as beingperformed by computer processor 28. For some applications, more than oneextraluminal imaging device is used with computer processor 28. Forexample, a first extraluminal imaging device may be used to acquire afirst set of extraluminal images, and a second extraluminal imagingdevice may be used to acquire a second set of extraluminal images.

Typically, computer processor 28 is configured to receive images of thesubject's body that have been processed by a computer processor 42 of animage-processing system 44. For some applications, images that have beenimage processed by the computer processor of the image-processing systemare displayed on a display 46 of the image-processing system.

FIG. 2 is an example of an extraluminal fluoroscopic image of asubject's chest that has been image processed by a computer processor ofan image-processing system (such as computer processor 42 ofimage-processing system 44), and that is received by computer processor28, in accordance with some applications of the present invention.Typically, image-processing system 44 artificially adds features to theimages that are acquired by one of the imaging devices (e.g.,extraluminal imaging device 20, and/or an endoluminal imaging device).For example, the artificially-added features may include features thatare added to identify the subject, to show measured data associated withthe subject, to identify the image processing system (for example, theimage may include a logo associated with the manufacturer of theimage-processing system), to classify the image as a certain type ofimage, or to perform a different function. The features may includealphanumeric characters, icons, pictures, and/or any other type or shapeof feature. Many medical imaging systems are configured to add suchfeatures (e.g., icons, and/or alphanumeric data) to images that havebeen acquired by an imaging device.

For some applications of the present invention, computer processor 28receives an image such as that shown in FIG. 2, and identifies(typically automatically) one or more features that are present withinthe image that were artificially added to the image, subsequent toacquisition of the image. Computer processor 28 generates an outputdevice on output device 40 in response to the removing the features.

For some applications, the output device is a display (as shown), andthe computer processor displays the image that was received from theimage-processing system, with the one or more features removed from theimage. For example, the features may be masked in the image that isdisplayed on the display. Alternatively or additionally, computerprocessor may be configured to identify portions of the image ascorresponding to portions of the subject's body (e.g., a blood vessel ofthe subject, or a lesion within a blood vessel) or a device within orupon the subject's body, and/or to perform measurements upon theidentified features. For some applications, before performing theaforementioned identifying and/or measurement steps, the computerprocessor identifies one or more features that are present within theimage that were artificially added to the image. In response thereto,when performing the identifying and/or measurement steps the computerprocessor takes into account the fact that the one or more features arenot features that were imaged by the imaging device.

For example, the computer processor may be configured to identifycenter-lines and/or edge lines of blood vessels within the image, toidentify a lesion within a blood vessel, and/or to perform quantitativeanalysis on the blood vessel (e.g., using techniques as described inU.S. Pat. No. 8,781,193 to Steinberg, which is incorporated herein byreference). Alternatively or additionally, the computer processor may beconfigured to identify devices that are placed inside the subject's body(e.g., using techniques as described in US 2014/0094691 to Steinbergand/or International Patent Application PCT/IL2015/050509 to Klaiman,both of which applications are incorporated herein by reference). Forsome such applications, computer processor 28 generates an output thatis indicative of quantitative analysis that is performed on the bloodvessel or the identified device, and/or drives the display to display animage, or a combination of images based upon having identified thevessel center-lines, vessel edge lines, the lesion, and/or the device.For example, the computer processor may coregister endoluminal data withextraluminal images at least partially based upon the identifiedfeatures, and may generate an output in response thereto, e.g., inaccordance with the techniques described in US 2012-0004537 to Tolkowskyand/or US 2014/0094691 to Steinberg, both of which applications areincorporated herein by reference. The computer processor may generate anoutput based upon the coregistration.

For some applications, before performing any one of the aforementionedsteps, computer processor identifies one or more features that arepresent within the image that were artificially added to the image. Inresponse thereto, the computer does not mistakenly identify suchfeatures as corresponding to an anatomical feature or a device that isdisposed inside or upon the subject's body. It is noted that it is oftenthe cases that artificially-added features include straight lines (e.g.,as in the case of alphanumeric characters). This being the case, theartificially-added features may be mistakenly identified ascorresponding to a portion of a blood vessel or a device, if thecomputer processor does not first identify the features as having beenartificially added to the image, e.g., using the techniques describedherein.

FIG. 3A-B are flowcharts showing steps of an algorithm that is performedby computer processor 28, in accordance with some applications of thepresent invention. With reference to FIG. 3A, in step 50, computerprocessor receives an image. As described hereinabove, for someapplications, computer processor receives the image from animage-processing system, such as system 44, which adds artificialfeatures to anatomical images of the subject's body. In step 52,computer processor 28 identifies the artificially-added feature(s), andin step 54, the computer processor generates an output, based uponhaving identified the feature(s) as having been artificially added.

With reference to FIG. 3B, for some applications, step 52 of FIG. 3A(i.e., the step of identifying artificially-added feature(s)) isperformed using some or all of the steps of the following algorithm.

For some applications, in step 60, computer processor selects one ormore regions within the image upon which to apply the further steps ofthe algorithm for identifying artificially-added feature(s) describedhereinbelow. Step 60 is shown inside a dashed box, to indicate that step60 is optional.

For some applications, further steps of the algorithm for identifyingartificially-added feature(s) are only applied to a portion of theimage. Typically, when image-processing systems artificially addfeatures to images, the features are added to the corners of the images.For example, FIG. 2 shows features that have been added thebottom-right, top-right, and top-left corners of the images. Therefore,for some applications, further steps of the algorithm for identifyingartificially-added feature(s) are only applied to pre-defined cornerregions of the image, or to pre-defined margins of the images. Forexample, the pre-defined margins may be defined as a pre-definedpercentage of the image (e.g., an upper 10 percent to 30 percent of theimage, and or a lower 10 percent to 30 percent of the image), or apre-defined number of pixels.

For some applications, computer processor is configured to receive aninput from a user that is indicative of a region to which to applyfurther steps of the algorithm for identifying artificially-addedfeature(s), and is configured to select the region in response thereto.Alternatively or additionally, the computer processor automaticallyselects the region upon which to apply further steps of the algorithmfor identifying artificially-added feature(s).

For some applications, computer processor is configured to apply one ormore filters to the selected region. It is noted that although threefilters are shown as being applied in parallel such as to generate threebinary images, and the binary images are then shown as being combinedinto a mask image (in step 68), for some applications, not all of thethree filters are applied. As such, the scope of the present inventionincludes applying any one of the filters, and/or any combinationthereof.

As shown, in step 62, the computer processor may apply a line-detectionfilter. For example, the artificially-added features may be whitealphanumeric characters. Therefore, for some applications, the computerprocessor uses a filter to identify sets of pixels that define a line,e.g., as described in U.S. Pat. No. 8,781,193 to Steinberg, which isincorporated herein by reference. For some applications, prior toapplying the line-detection filter, the computer processor inverts theimage, such that the bright lines of text appear dark. For someapplications, the output of applying the filter is a binary image inwhich the identified lines are assigned a first value, and other pixelswithin the image are assigned a second value.

Reference is now made to FIG. 4A, which shows an example of a binaryimage generated by applying a line-detection filter as described aboveto the image shown in FIG. 2. The identified lines are white and otherpixels within the image are black.

Referring again to FIG. 3B, as shown in step 64, the computer processormay apply a line-density filter. For some applications, as analternative to or in addition to identifying sets of pixels that definelines within the region(s) selected in step 60, the computer processorapplies a filter such as to identify regions of the image within which adensity of straight lines exceeds a given threshold. For someapplications, the output of applying the filter is a binary image inwhich the regions of the image within which a density of straight linesexceeds a given threshold are assigned a first value, and other pixelswithin the image are assigned a second value.

Reference is now made to FIG. 4B, which shows an example of a binaryimage generated by applying a line-density filter as described above tothe image shown in FIG. 2. The identified regions are white and otherpixels within the image are black.

Referring again to FIG. 3B, as shown in step 64, the computer processormay apply a directional-gradient-density filter. For some applications,as an alternative to, or in addition to, applying steps 62 and 64 withinthe region(s) selected in step 60, the computer processor applies adirectional-gradient-density filter to the region. For someapplications, a Sobel filter is applied to the region, in order toextract horizontal and/or vertical gradients. Each of the directionalgradients images is then filtered with a large box filter to findregions with an amount of directional gradients that exceeds athreshold. For some applications, the directional gradient images arecombined with an AND operator to find regions with both horizontal andvertical gradients that exceed respective thresholds. For someapplications, the order in which the aforementioned steps are applied isdifferent to that described above. For example, the AND operator stepmay be applied before the thresholding step is applied. For someapplications, the output of applying the directional-gradient-densityfilter is a binary image, in which the regions of the image within whicha density of directional gradients exceeds a given threshold areassigned a first value, and other pixels within the image are assigned asecond value.

Referring again to FIG. 3B, for some applications a single mask image isgenerated in step 68. For some applications, one or more of steps 62,64, and 68 are applied in parallel, and the binary image(s) that aregenerated by applying these steps are combined into a single mask image,e.g., using an AND operator. For some applications, in step 70 the maskthat is outputted from step 68 is dilated, e.g., such as to provide asafety margin.

Reference is now made to FIG. 4D, which is a mask image that wasgenerated by combining the binary images shown in FIGS. 4A-C and thendilating the resulting mask, in accordance with some applications of thepresent invention. Typically, in step 72 of FIG. 3B, the mask that isgenerated is applied to the original image. Regions of the originalimage that are within the mask are identified as corresponding toartificially-added features, and features that are not within the maskare not. Typically, in step 54 of FIGS. 3A and 3B, an output isgenerated in response to identifying the artificially-added features,e.g., as described hereinabove.

Reference is now made to FIG. 5, which is a flowchart showing steps ofan algorithm that is performed by a processor, in accordance with someapplications of the present invention. For some applications, step 52 ofFIG. 3A (i.e., the step of identifying artificially-added feature(s)) isperformed using some or all of the steps of the following algorithm.

For some applications, in step 80, computer processor 28 selects one ormore regions within the image upon which to apply the further steps ofthe algorithm for identifying artificially-added feature(s) as describedhereinbelow. Step 80 is shown inside a dashed box, to indicate that step80 is optional. Step 80 is performed in a generally similar manner tostep 60 described hereinabove with reference to FIG. 3B.

In step 82, the computer processor identifies a first pixel an intensityof which differs from the intensity of one or more pixels in a vicinityof the first pixel by more than a threshold amount. Typically, this isan indication that the pixel may correspond, for example to a whitealphanumeric character (or other symbol) that has been artificiallyadded to a region of the image that has a generally dark background.

Typically, features that are added automatically to images are added tothe same place in each of a set of images that is outputted by an imageprocessing system. For example, if the manufacturer of theimage-processing system adds their logo to each of the images, the logois typically added to the same place in each of the images. Or, if thesubject's name is added to the images, then the name is typically addedto the same place in each of the images. Therefore, in step 84, thepixel that was identified as potentially corresponding to anartificially-added feature in step 82 is identified in one or moreadditional images, and the computer processor determines whether thedifference between the value of the pixel in the images differs by lessthan a threshold amount. In response to the detecting that thedifference is less than a threshold amount, the computer processoridentifies the feature as corresponding to an artificially-addedfeature. For some applications, steps 82 and 84 are performed in reverseorder.

In step 86, the computer processor generates a mask in the region of apixel that has been identified as corresponding to an artificially-addedfeature. For some applications, in step 88, the computer processordilates the resultant mask. It is noted that, typically, steps 82, 84,and 86 are applied to more than one pixel within the region selected instep 80. Typically, the computer processor applies steps 82, 84 and 86to a plurality of pixels (e.g., all of the pixels) within the regionselected in step 80, such as to identify all pixels within the regionthat (a) differ in intensity from the intensity of a pixel within thevicinity by more than a threshold amount, and (b) differ in value fromthe value of the pixel in one or more additional images by less than athreshold amount. In this manner, all pixels that correspond toartificially-added features are identified.

Typically, in step 90 the mask that is generated is applied to theoriginal image. Regions of the original image that are within the maskare identified as corresponding to artificially-added features, andfeatures that are not within the mask are not. Typically, in step 54, anoutput is generated in response to identifying the artificially-addedfeatures, as described hereinabove.

It is noted that although some techniques described herein are describedprimarily with respect to extraluminal fluoroscopic/angiographic images,the scope of the present invention includes applying the techniquesdescribed herein to other forms of extraluminal images, mutatismutandis. For example, the extraluminal images may include imagesgenerated by fluoroscopy, CT, MRI, ultrasound, PET, SPECT, otherextraluminal imaging techniques, or any combination thereof. Endoluminalimages may include images generated by intravascular ultrasound (IVUS)optical coherence tomography (OCT), near-infrared spectroscopy (NIRS),intravascular ultrasound (IVUS), endobronchial ultrasound (EBUS),magnetic resonance (MR), other endoluminal imaging techniques, or anycombination thereof. Endoluminal data may include data related topressure (e.g., fractional flow reserve), flow, temperature, electricalactivity, or any combination thereof.

Although some techniques described herein are described primarily asbeing performed on a blood vessel, the scope of the present applicationincludes performing similar techniques on a lumen in the vascularsystem, the respiratory tract, the digestive tract, the urinary tract,any other luminal structure within a patient's body, or any othersuitable anatomical structure within a patient's body, mutatis mutandis.Examples of an anatomical structure to which the techniques describedherein may be applied include a coronary vessel, a coronary lesion, avessel, a vascular lesion, a lumen, a luminal lesion, and/or a valve.

Applications of the invention described herein can take the form of acomputer program product accessible from a computer-usable orcomputer-readable medium (e.g., a non-transitory computer-readablemedium) providing program code for use by or in connection with acomputer or any instruction execution system, such as computer processor28. For the purposes of this description, a computer-usable or computerreadable medium can be any apparatus that can comprise, store,communicate, propagate, or transport the program for use by or inconnection with the instruction execution system, apparatus, or device.The medium can be an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system (or apparatus or device) or apropagation medium. Typically, the computer-usable or computer readablemedium is a non-transitory computer-usable or computer readable medium.

Examples of a computer-readable medium include a semiconductor or solidstate memory, magnetic tape, a removable computer diskette, a randomaccess memory (RAM), a read-only memory (ROM), a rigid magnetic disk andan optical disk. Current examples of optical disks include compactdisk-read only memory (CD-ROM), compact disk-read/write (CD-R/W) andDVD.

A data processing system suitable for storing and/or executing programcode will include at least one processor (e.g., computer processor 28)coupled directly or indirectly to memory elements (e.g., memory 29)through a system bus. The memory elements can include local memoryemployed during actual execution of the program code, bulk storage, andcache memories which provide temporary storage of at least some programcode in order to reduce the number of times code must be retrieved frombulk storage during execution. The system can read the inventiveinstructions on the program storage devices and follow theseinstructions to execute the methodology of the embodiments of theinvention.

Network adapters may be coupled to the processor to enable the processorto become coupled to other processors or remote printers or storagedevices through intervening private or public networks. Modems, cablemodem and Ethernet cards are just a few of the currently available typesof network adapters.

Computer program code for carrying out operations of the presentinvention may be written in any combination of one or more programminglanguages, including an object oriented programming language such asJava, Smalltalk, C++ or the like and conventional procedural programminglanguages, such as the C programming language or similar programminglanguages.

It will be understood that each block of the flowcharts shown in FIGS.3A-B and 5 and combinations of blocks in the flowchart, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer (e.g., computerprocessor 28) or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartsand/or algorithms described in the present application. These computerprogram instructions may also be stored in a computer-readable medium(e.g., a non-transitory computer-readable medium) that can direct acomputer or other programmable data processing apparatus to function ina particular manner, such that the instructions stored in thecomputer-readable medium produce an article of manufacture includinginstruction means which implement the function/act specified in theflowchart blocks and algorithms. The computer program instructions mayalso be loaded onto a computer or other programmable data processingapparatus to cause a series of operational steps to be performed on thecomputer or other programmable apparatus to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowcharts and/oralgorithms described in the present application.

Computer processor 28 is typically a hardware device programmed withcomputer program instructions to produce a special purpose computer. Forexample, when programmed to perform the algorithms described withreference to FIGS. 3A-B and 5, computer processor 28 typically acts as aspecial purpose feature-identification computer processor. Typically,the operations described herein that are performed by computer processor28 transform the physical state of memory 29, which is a real physicalarticle, to have a different magnetic polarity, electrical charge, orthe like depending on the technology of the memory that is used.

The terms “medical tool,” “tool”, “device,” and “probe” as used in thespecification and the claims of the present application may refer to anytype of a diagnostic or therapeutic or other functional tool. By way ofexample, such tools may include a cardiovascular catheter, a stentdelivery, placement and/or retrieval tool, a balloon delivery and/orplacement and/or retrieval tool, a valve delivery and/or repair and/orplacement and/or retrieval tool, a graft delivery and/or placementand/or retrieval tool, a tool for the delivery and/or placement and/orretrieval of an implantable device or of parts of such device, animplantable device or parts thereof, a tool for closing a gap, a toolfor closing a septal defect, a guide wire, a marker wire, a suturingtool, a clipping tool (such as a valve-leaflet-clipping tool), a biopsytool, an aspiration tool, a navigational tool, a localization tool, aprobe comprising one or more location sensors, a tissue characterizationprobe, a probe for the analysis of fluid, a measurement probe, anelectrophysiological probe, a stimulation probe, an ablation tool, atool for penetrating or opening partial or total occlusions in bloodvessels, a drug or substance delivery tool, a chemotherapy tool, aphotodynamic therapy tool, a brachytherapy tool, a local irradiationtool, a laser device, a tool for delivering energy, a tool fordelivering markers or biomarkers, a tool for delivering biological glue,an irrigation device, a suction device, a ventilation device, a devicefor delivering and/or placing and/or retrieving a lead of anelectrophysiological device, a lead of an electrophysiological device, apacing device, a coronary sinus device, an imaging device, a sensingprobe, a probe comprising an optical fiber, a robotic tool, a tool thatis controlled remotely, an excision tool, a plaque excision tool (suchas a plaque excision catheter), or any combination thereof.Alternatively, the terms “medical tool,” “tool”, “device,” and “probe”as used in the specification and the claims of the present applicationmay refer to a different type of tool and/or medical tool.

The terms “image” and “imaging” as used in the specification and theclaims of the present application may refer to any type of medicalimages or imaging, typically resulting in the generation of a sequenceof images. For example, such imaging may include imaging using ionizingradiation, imaging using non-ionizing radiation, video, fluoroscopy,angiography, ultrasound, CT, MR, PET, PET-CT, CT angiography, SPECT,Gamma camera imaging, Optical Coherence Tomography (OCT), Near-Infra-RedSpectroscopy (NIRS), Vibration Response Imaging (VRI), optical imaging,infrared imaging, electrical mapping imaging, other forms of functionalimaging, Focused Acoustic Computed Tomography (FACT), Optical FrequencyDomain Imaging (OFDI), or any combination or fusion thereof. Examples ofultrasound imaging may include Endo-Bronchial Ultrasound (EBUS),Trans-Thoracic Echo (TTE), Trans-Esophageal Echo (TEE), Intra-VascularUltrasound (IVUS), Intra-Cardiac Ultrasound (ICE), or any combinationthereof. Alternatively, the terms “image” and “imaging” as used in thespecification and the claims of the present application may refer toimaging using a different imaging modality from the above-describedimaging modalities.

The term “contrast agent,” as used in the specification and the claimsof the present application may include any substance that is used toenhance the visibility of the anatomical structure, functioning, and/orcomposition of a bodily organ while the organ is being imaged, e.g., byhighlighting the anatomical structure, functioning, and/or compositionof a bodily organ.

The scope of the present application includes combining the apparatusand methods described herein with apparatus and methods described in anyone of the following applications, all of which are incorporated hereinby reference:

-   -   International Application PCT/IL2008/000316 to Iddan (published        as WO 08/107905), filed Mar. 9, 2008, entitled “Imaging and        tools for use with moving organs.”    -   U.S. patent application Ser. No. 12/075,252 to Iddan (published        as US 2008/0221440), filed Mar. 10, 2008, entitled “Imaging and        tools for use with moving organs;”    -   International Application PCT/IL2009/000610 to Iddan (published        as WO 09/153794), filed Jun. 18, 2009, entitled “Stepwise        advancement of a medical tool;”    -   U.S. patent application Ser. No. 12/487,315 to Iddan (issued as        U.S. Pat. No. 8,700,130), filed Jun. 18, 2009, entitled        “Stepwise advancement of a medical tool;”    -   U.S. patent application Ser. No. 12/666,879 to Steinberg (issued        as U.S. Pat. No. 8,781,193), which is the US national phase of        PCT Application No. PCT/IL2009/001089 to Cohen (published as WO        10/058398), filed Nov. 18, 2009, entitled “Image processing and        tool actuation for medical procedures;”    -   U.S. patent application Ser. No. 12/781,366 to Cohen (published        as US 2010/0222671), filed May 17, 2010, entitled        “Identification and presentation of device-to-vessel relative        motion;”    -   International Patent Application PCT/IL2011/000391 to Cohen        (published as WO 11/145094), filed May 17, 2011, entitled        “Identification and presentation of device-to-vessel relative        motion;”    -   U.S. Ser. No. 13/228,229 to Tolkowsky (published as US        2012/0004537), filed Sep. 8, 2011, which is a continuation of        International Application No. PCT/IL2011/000612 to Tolkowsky        (published as WO 12/014212), filed 28 Jul. 2011 entitled “Co-use        of endoluminal data and extraluminal imaging;”    -   U.S. patent application Ser. No. 14/128,243 to Barzelay        (published as US 2014/0140597), which is the US national phase        of International Patent Application PCT/IL2012/000246 (published        as WO 12/176191), filed Jun. 21, 2012, entitled “Luminal        background cleaning;”    -   U.S. patent application Ser. No. 14/097,922 to Steinberg        (published as US 2014/0094691), filed Dec. 5, 2013, entitled        “Co-use of endoluminal data and extraluminal imaging,” which is        a continuation of International Application PCT/IL2013/050438        (published as WO 13/175472) to Steinberg, filed May 21, 2013,        entitled “Co-use of endoluminal data and extraluminal imaging;”    -   U.S. patent application Ser. No. 14/142,082 to Tolkowsky        (published as US 2014/0121513), filed Dec. 27, 2013, entitled        “Determining a characteristic of a lumen by measuring velocity        of a contrast agent,” which is a continuation of International        Application PCT/IL2013/050549 (published as WO 14/002095) to        Tolkowsky, filed Jun. 26, 2013, entitled “Flow-related image        processing in luminal organs;”    -   International Patent Application PCT/IL2015/050372 to Klaiman,        filed Apr. 2, 2015, entitled “Image analysis in the presence of        a medical device,” which claims priority from U.S. Provisional        Patent Application 61/977,891 to Klaiman, filed Apr. 10, 2014,        entitled “Image analysis in the presence of a medical device;”        and    -   International Patent Application PCT/IL2015/050509 to Klaiman,        filed May 13, 2015, entitled “Object identification,” which        claims priority from US Provisional Patent Application        61/993,123 to Klaiman, filed May 14, 2014, entitled “Image        analysis in the presence of a medical device.”

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed hereinabove. Rather, the scope of the present inventionincludes both combinations and subcombinations of the various featuresdescribed hereinabove, as well as variations and modifications thereofthat are not in the prior art, which would occur to persons skilled inthe art upon reading the foregoing description.

The invention claimed is:
 1. A method comprising: receiving, via atleast one computer processor, at least one image of a portion of asubject's body, wherein the image includes a feature that wasartificially added subsequent to acquisition of the image; using the atleast one computer processor, identifying the feature within the image,wherein identifying the feature comprises: comparing a first differencein intensity between a first pixel of the image and a second pixel ofthe image to a first threshold, wherein the second pixel is within agiven distance from the first pixel; and identifying a region of theimage that contains the first pixel as containing the feature, based oncomparing the first difference and the first threshold; and in responsethereto, generating an output on an output device, wherein generatingthe output comprises driving a display to display the image with thefeature removed from the image.
 2. The method according to claim 1,further comprising, using the computer processor, performingmeasurements upon the image, by excluding the identified feature frombeing included in the measurements, wherein generating the outputcomprises generating an indication of the measurements upon the outputdevice.
 3. The method according to claim 1, wherein identifying thefeature further comprises determining that the feature is located withina given distance of an edge of the image, and identifying the feature ashaving been artificially added to the image, subsequent to acquisitionof the image.
 4. The method according to claim 1, wherein identifyingthe feature further comprises identifying alphanumeric characteristicsthat are present within the image.
 5. The method according to claim 1,wherein identifying the feature further comprises identifying a set ofpixels as defining a line and identifying the set of pixels ascorresponding to the feature.
 6. The method according to claim 1,wherein identifying the feature further comprises identifying a regionof the image within which a density of straight lines exceeds athreshold and identifying the region as containing the feature.
 7. Themethod according to claim 1, wherein identifying the feature furthercomprises determining that a density of horizontal and verticalgradients within a given region of the image exceeds a threshold andidentifying the region as containing the feature.
 8. The methodaccording to claim 1, wherein identifying the feature further comprises:comparing a second difference in intensity between the first pixel inthe image and the first pixel in one or more additional images of theportion of the subject's body to a second threshold; and identifying aregion that contains the first pixel as containing the feature, based onthe comparing the second difference and the second threshold. 9.Apparatus comprising: an imaging device configured to acquire an imageof a portion of a body of a subject; an output device; and at least onecomputer processor configured to: receive, from the imaging device, theimage of the portion of the subject's body, wherein the image includes afeature that was artificially added subsequent to acquisition of theimage; identify the feature within the image by: comparing a firstdifference in intensity between a first pixel of the image and a secondpixel of the image to a first threshold, wherein the second pixel iswithin a given distance from the first pixel; and identifying a regionof the image that contains the first pixel as containing the feature,based on comparing the first difference and the first threshold; and inresponse thereto, generate an output on the output device by driving adisplay to display the image with the feature removed from the image.10. The apparatus according to claim 9, wherein the computer processoris configured to perform measurements upon the image, by excluding theidentified feature from being included in the measurements, and whereinthe computer processor is configured to generate the output bygenerating an indication of the measurements upon the output device. 11.The apparatus according to claim 9, wherein the computer processor isfurther configured to identify the feature by determining that thefeature is located within a given distance of an edge of the image, andidentifying the feature as having been artificially added to the image,subsequent to acquisition of the image.
 12. The apparatus according toclaim 9, wherein the computer processor is further configured toidentify the feature by identifying alphanumeric characteristics thatare present within the image.
 13. The apparatus according to claim 12,wherein the computer processor is further configured to identify thefeature by at least one of: identifying a set of pixels as defining aline and identifying the set of pixels as corresponding to the feature;identifying a region of the image within which a density of straightlines exceeds a threshold and identifying the region as containing thefeature; and determining that a density of horizontal and verticalgradients within a given region of the image exceeds a threshold andidentifying the region as containing the feature.
 14. The apparatusaccording to claim 12, wherein the computer processor is furtherconfigured to identify the feature by: comparing a second difference inintensity between the first pixel in the image and the first pixel inone or more additional images of the portion of the subject's body to asecond threshold amount; and identifying a region that contains thefirst pixel as containing the feature, based on comparing the seconddifference and the second threshold.
 15. A computer software product,for use with an imaging device configured to acquire an image of aportion of a body of a subject, and an output device, the computersoftware product comprising a non-transitory computer-readable medium inwhich program instructions are stored, which instructions, when read bya computer cause the computer to perform the steps of the methodaccording to claim
 1. 16. The apparatus according to claim 9, whereinthe computer processor is configured to identify the feature bydetermining that the first difference exceeds the first threshold. 17.The apparatus according to claim 14, wherein the computer processor isconfigured to identify the feature by determining that the seconddifference is less than the second threshold.